1. Field of Invention
The present invention relates to a booster and a voltage detection method thereof, and more particular, to a booster that detects a power source thereof to efficiently generate a target voltage.
2. Description of Related Art
In an electronic device, a plurality of charge pump circuits are usually required for providing various power voltage levels. The charge pump circuit uses capacitors as energy storage elements and uses switching devices to control the connection of voltages to the capacitors. FIG. 1A is a diagram of a charge pump circuit providing a double positive voltage. Referring to FIG. 1A, during a charge period, switches 101 and 102 are turned on, and switches 103 and 104 are turned off. An input voltage VIN and a ground voltage GND are respectively coupled to two terminals of a capacitor 105, and charge the capacitor 105, so that a voltage difference between the terminals N1 and N2 of the capacitor 105 is the input voltage VIN. During a pump period, the switches 101 and 102 are turned off, and the switches 103 and 104 are turned on. At present, the voltage level of the terminal N2 of the capacitor 105 rises from the original ground voltage GND to the input voltage VIN, and the voltage level of the terminal N1 of the capacitor 105 rises from the original input voltage VIN to the double input voltage 2×VIN, i.e. an output voltage VOUT+=2×VIN, since the voltage difference between the terminals N1 and N2 of the capacitor 105 is the input voltage VIN.
FIG. 1B is a diagram of a charge pump circuit providing a negative voltage. Referring to FIG. 1B, during a charge period, switches 106 and 107 are turned on, and switches 108 and 109 are turned-off. An input voltage VIN and a ground voltage GND are respectively coupled to two terminals of a capacitor 110, and charge the capacitor 110, so that a voltage difference between the terminals N3 and N4 of the capacitor 110 is the input voltage VIN. During a pump period, the switches 106 and 107 are turned off, and the switches 108 and 109 are turned on. At present, the voltage level of the terminal N3 of the capacitor 110 drops from the original input voltage VIN to the ground voltage GND, and the voltage level of the terminal N4 of the capacitor 110 drops from the ground voltage GND to the negative input voltage −VIN, i.e. an output voltage VOUT−=−VIN, since the voltage difference between the terminals N3 and N4 of the capacitor 110 is the input voltage VIN.
The charge pump circuit can provide the output voltages with different times as large as the input voltage VIN, e.g. −1, 1.5, 2, and 3 times. If the input voltage VIN is 3 volts and the target output voltage is 4.2 volts, the charge pump circuit would efficiently generate the output voltage with 1.5 times as large as the input voltage VIN. In addition, if the target output voltage is 6 volts, the charge pump circuit would efficiently generate the output voltage with 2 times as large as the input voltage VIN, rather than the output voltage with 3 times as large as the input voltage VIN. However, the input voltage VIN may drop as time passes by, and the output voltage may drop when a load of the charge pump circuit increases. The charge pump circuit should efficiently generate the output voltage with proper times as large as the input voltage, to be close to the target output voltage.